Here's thought for immersion. Scrap the waiting for players, death match idea. Have 30 - 40player severs, with access to visiting the entire map, when and where they want. The players on that sever theoretically live there. This opens up a sense of the unknown, and would add an element of true survival. Have the radiation sweeps sporadic, providing bunkers for escape. It would become aliving breathig world with players battling to stay alive.
It worries me that this is more of a buisness move to jump on the success of the battle royal genre rather than developing this fantastic idea to its true potential.